Duplicate files on HD

So, I really want to pull my hair out trying to "clean up" my fiance's family's computer. Its an old POS Sony Vaio. Its got a P4 1.5Ghz, 512MB RAM, a 15 and a 40GB HDs.

I just upgraded them to 512MB ram, installed.
I bought a new 80GB Seagate because they had filled the other hard drives completely.

I spent the last few hours copying over all of the personal documents (pics, music, etc) from the C to the D drive because I was going to remove the 15GB and replace it with the 80 and do a fresh install of windows.

When I cracked the case open, there was 1 HD... It is just partitioned! Now I have a ton of duplicate files on this old HD which is almost completely full now.

I would really like to scrub the drive and remove all the duplicate items to free up space and make it less cluttered. I would ideally like to do a fresh reinstall of windows on the 80 then transfer all the personal files over to that drive, format the old one, and set it up so that it does not show up as a second drive, just added onto the (new) C drive, if that is possible.

Any and all help and advice would be great. I would really like to complete this project tomorrow. Thanks in advance!

To search for duplicate file under windows operating system I suggest a freeware called Easy Duplicate File Finder.
Check their website at:
www.easyduplicatefinder.com
make sure you know what you are doing before you delete any files.

to prevent the problem of eliminate important files, I think, what I'll do is:
1. uninstall (Hardware) the partitioned HDD (within minutes)
2. install (Hardware) your new 80GB HDD, (within minutes)
3. install (Software) OS, programs, updates, etc.. (probably several hours, depends on what will be installed and sometimes the internet speed)
4. install (Hardware) the old HDD (minutes)
5. copy files/setups from old HDD to new HDD (maybe an hour?)
6. find duplicate in new HDD and remove them (can't say how long will this take.)
7. remove (Hardware) the old HDD again. (Don't format it, unless you really need that space.)
If you live far-far away, ask for permission to bring the old HDD away with you so that you can e-mail them the files if they were accidentally removed during step 6, or make sure there is someone knows how to install (hardware) the HDD and restore the missing file if it so occurred.
8. let the owners check and run the system for a while and see if there is anything missing before you even think about format the old HDD.

Good luck

I can still use the old HDD along with the new one for extra space right? Is there a way to have it installed so that its space is just added to the C drive, instead of having a separate D drive?

Yes, but my point (to keep all the files in the old HDD) is depend on: Data/files/time is more valuable than disk space.
Consider this:
New 500GB HDD you probably need to pay $120 these days.
Your 60G (warranty expired and used) HDD probably worth maybe $15-30 on e-bay.
The only copy of some family pictures in that HDD... PRICELESS


Yes, you may use RAID 0 or stripe disk (whether its software or hardware based)
or based on M$' 2k/Xp/2K3/Vi... let it became a subfolder.

Helpful info...Thanks